The field of the present invention is that of automotive engines, in particularly automotive engines having deceleration fuel shut off.
Deceleration fuel shut off (DFSO) can lead up to four percent fuel savings on the combined Federal Test Procedure cycle. Even greater fuel savings are possible with drive cycles which include more deceleration time. However, in the past there have been particular technical problems in implementing DFSO. One of the problems in implementing DFSO is transient fuel behavior in the intake system. Transient fuel behavior can be alleviated with direct in-cylinder fuel injection or more advanced port fuel injection systems with less wall wetting. A second problem in implementing DFSO is the more intense vehicle deceleration due to increased braking by the engine. The problem of increased braking by the engine can be resolved by increased driver acclimation and by acknowledgement of the benefit of less stress and wear upon the vehicle braking system. The third issue and the hardest technical challenge to overcome is the issue of excessive air being pumped to the engine exhaust system. Excessive air causes cooling and oxygen loading of the exhaust system catalyst under normal DFSO conditions.
It is desirable to provide an internal combustion engine and a method of operation thereof which allows DFSO. It is also desirable to provide an arrangement of an internal combustion engine and a method of operation thereof which allows DFSO without causing cooling or excessive oxygen loading of the vehicle catalyst in order to avoid degrading the NOx conversion efficiency of the catalyst upon subsequent engine operation. It is further desirable to provide an internal combustion engine and a method of operation thereof with the above-noted features which can also be utilized to provide engine braking when high levels of vehicle deceleration are desired.
To make manifest the above-delineated and other desires the revelation of the present invention is brought forth. In the arrangement of the internal combustion engine of the present invention, the intake event of the cylindrical combustion chamber intake poppet valves is phased to be symmetric about the top dead center (phase advanced) or preferably the bottom dead center (phase retarded) position. Equal amounts of airflow are pulled into the combustion chamber via the intake valve opening during the intake stroke and expelled through the intake valve opening from the combustion chamber during the first part of the compression stroke minimizing pumping work. The exhaust poppet valve is deactivated. Accordingly, during this period of deceleration, the fuel can be shut off from the vehicle. If additional braking is required, the intake cam can be advanced to standard timing. The advancement of the intake cam to standard timing increases pumping work and engine braking.
It is a feature of the present invention to provide a four-cycle internal combustion engine arrangement that has DFSO by disabling the exhaust valve on the deactivated cylinder(s) to a closed position and phase varying the operation of the intake poppet valve.
The above noted object and other features of the present invention will become better known to one skilled in the art from a review of the accompanying drawings and detailed description of the invention.